This study reports a leaching process along with a novel physical pretreatment technique to remove iron impurities from kaolin using oxalic acid. A detailed examination of the physical properties of the minerals confirmed that almost none of the leaching-resistant iron oxides, specifically hematite, was completely interlocked with the clay minerals. Accordingly, a pre-agitating technique followed by high-pressure washing of the sample on a 600 μm sieve were applied. In this method, by discarding up to 20% of the raw material, >54% of the total iron content of the raw kaolin was removed, and the iron content was reduced from 9.75% in the initial sample to <6.00% in the passing fraction. Application of this pretreatment method rendered the leaching process successful at 97°C using 0.3 M oxalic acid solutions for 1 h under atmospheric pressure. Compared to the leaching of the raw material without pretreatment, which consumed at least 0.5 M oxalic acid over a minimum period of 2 h, the method used was very cost-effective and favourable, reducing the iron content of the product to <1% and producing high-quality kaolin.

Natural tuff samples in western Anatolia (Türkiye) originating from Miocene rhyolitic–pyroclastic rocks with >80 wt.% heulandite/clinoptilolite zeolites were investigated for their surface characteristics determined according to nitrogen adsorption after degassing at 150°C (specific surface area, pore volume and pore diameter). Additionally, these surface characteristics were correlated with the cationic compositions of the heulandite/clinoptilolite group minerals. The examined samples were characterized by two main pore diameters that were not related to specific surface area and pore volume but were partially related to the types and occupancy of extra-framework cations. One set of samples has a pore diameter of ~24 Å, total cation content (Na + K + Ca + Mg) ranging from 3.46 to 4.40 and a (Na + K)/(Ca + Mg) ratio ranging from 0.34 to 0.92. The total cation contents and (Na + K)/(Ca + Mg) ratios of the remaining samples with a pore diameter of ~37 Å are 4.30–5.08 and 1.48–2.85, respectively. After degassing at 300°C, there is a slight difference in the pore diameters of these two sets of samples (~37 and 38 Å). The pore sizes of the samples with a (Na + K)/(Ca + Mg) ratio < 1 (heulandite composition) increased from 24 to 36–38 Å with increasing degassing temperature, whereas the pore sizes of the samples with a (Na + K)/(Ca + Mg) ratio > 1 (clinoptilolite composition) increased from 37 to only 38–39 Å. However, there is no correlation between the Si/Al ratios and the cation-exchange capacities of the samples and their surface characteristics obtained by degassing at the two temperatures.

Study of “tierras de Lebrija” by chemical, dehydration curves, d.t.a., X-ray and electron microscopic methods indicates the composition of these Pliocene sediments to be approximately equal quantities of attapulgite and illite.

The industrial uses of clay minerals as catalysts date from the early 'thirties. The application of catalysis to the thermal cracking of oil started in about 1931; pre-heated oil was passed downwards through fixed beds of granular catalyst, often attapulgite, under pressure (80 lb. per sq. in.) and at about 900°F., as in the Houdry and Hydroforming systems. The catalyst had to be periodically burned off to regenerate it, and was reintroduced at the top of the reaction column. An improvement on this static process came when the granulated catalyst was kept moving counter current to the pre-heated oil. This led about 1939 to the fluid-flow method of catalysis in which powdered catalysts are used in a fluid, free-flowing condition, circulated by the air-rift method well-known in the movement of liquids.

La composition minéralogique de la phase <2 µm de la croûte d'altération de teinte pâele et de quelques millimétres d'épaisseur, développée sur les faces des prismes basaltiques de Roudadou, près d'Aurillac, Cantal, a été étudiée par plusieurs techniques: RX, analyse thermique différentielle, thermogravimétrie, spectroscopie infra-rouge entre 600 et 200 cm−1, mesure des surfaces totales. Cette phase fine est constituée d'une fraction non cristalline relativement réduite et surtout de minéraux argileux cristallisés, parmi lesquels l'imogolite est largement dominante (50%), accompagnée de l'halloysite (30%). Parfois une smectite compléte ce cortège argileux. A notre connaissance, l'imogolite n'avait jamais été identifiée parmi les produits d'altération superficielle des roches volcaniques du Massif Central.

Preliminary investigation of the minerals in sediment core 15 taken at a depth of 1990 metres in the Gulf of Naples shows:

1. (i) Volcanic materials, especially glass, occur throughout the core, but only in certain horizons >50%. These horizons represent periods of volcanic activities in the region and further investigation is required to correlate them.

2. (ii) No mineral in the core shows any post-depositional alteration, and most of them are clear and fresh.

3. (iii) Among the clay minerals illite is predominant, but kaolinite and mont-morillonite are also present.

The catalytic cracking process, which first came into prominence during the recent war, was one of the means adopted by the petroleum industry to meet the demand for aviation spirit of high quality to fuel the Allies' air forces. It was applied mainly in the United States and quantitatively made the largest contribution of any process. The process is a modification of the older thermal cracking process, the presence of the catalyst bringing about at a lower temperature the breakdown of large hydrocarbon molecules into smaller ones (some in the petrol boiling range) whilst at the same time promoting side reactions which improve the quality of the spirit.

The search for sufficiently high-quality clays for use in the tile industry represents a significant challenge. This study aimed to prepare Muttalip green clay tiles with flexural strengths adhering to the TS EN 1304:2016 standard. Muttalip green clay was subjected to sieving, vacuum pressed, dried and then baked to obtain galette tiles. The tiles were analysed subsequently using optical techniques, including X-ray diffraction, X-ray fluorescence spectrometry and field-emission scanning electron microscopy. The influence of various firing temperatures (900, 950 and 1000°C) on the flexural strength of the tiles was also investigated. The tiles obtained at 950°C exhibited a maximum flexural strength of 153.91 kg cm–2. Fourier-transform infrared spectroscopy revealed that the tiles reflect ultraviolet A radiation and absorb infrared radiation. Muttalip green clay is a suitable material for preparing tiles for roofing applications.

The matric potential of water in gels of five-sixths neutralized aluminium montmorillonite (bentonite) and aluminium kaolinite changes during periods of shear and periods of rest. Shear increases the potential of water in bentonite gels, and in kaolinite gels containing little water, but decreases the potential in kaolinite gels containing more water. All these effects can be explained by changes in the curvature of water films at the gel-air interface. The difference between thixotropic and dilatant behaviour is the increasing and decreasing of the water potential on shearing. In dilatant pastes of silt-size particles, and for which the effects of electric charges are small, the pressure deficiency can reach large values after an increase in pore space, and this suffices to explain the characteristic features of dilatant behaviour.

Aung et al. (2014, 2015) described the activation of kaolin samples to remove coloured pigments from rice-bran oil, the effects of various treatments on their decolourization capacity, and the characterization of these kaolin samples by physical methods. This research used a kaolin sample from Ranong in southern Thailand, and investigated the effects of grinding and heat treatment prior to acid activation of the mineral. The various activated mineral phases were then characterized by a combination of X-ray diffraction, Fourier-Transform infrared spectroscopy and X-ray fluorescence. This work represented an extension of research reported previously by Worasith et al. (2011a), in which various samples of the same Ranong kaolin were characterized after grinding and acid activation, and their capacities to decolourize rice-bran oil evaluated (Worasith et al., 2011b). However, despite the similarities in the experiments, there are some important differences in the results presented in these two sets of publications, which raise questions concerning the conduct of this type of research and the generality of any conclusions derived.

L'étude de la conductivité hydraulique sous de faibles charges de pâtes et de gels d'hectorite-Na, montre que:

• 1. La loi de Darcy peut être appliquée,

• 2. Le rayon hydraulique moyen qui est probablement relié à la distance moyenne entre les particules d'hectorite varie linéairement avec la teneur en eau et est très sensible à la présence d'électrolyte dans la suspension.

After the last retreat of the corrie glaciers in the Ice Age the Mesozoic deposits lying at the foot of the Tertiary basalt cliffs in the Trotternish peninsula of Skye were subjected to substantial landsliding movements towards the sea. A number of lochs were held up partly by the moraines and partly by reverse slopes caused by the landslides. In a number of these lochs, after a period of partial filling by silt, diatomite has been deposited. Most of the deposits are covered with two to four feet of peat. We may roughly estimate the period of diatomite deposition to have been from about 10,000 to about 2,000 years ago. It is hoped to date the deposit accurately when samples have been examined by pollen analysis.